A pump device of a rotary type for a vehicle brake control system is known in the art, for example, as disclosed in Japanese Patent Publication No. 2007-125929, according to which a force is generated by a spring member in an axial direction in order not only to restrict a movement of a pump body (in which rotary pumps for two hydraulic systems are accommodated) in the axial direction thereof but also to prevent a pump casing of the pump body from being damaged by internal pressure of brake fluid discharged from the rotary pumps at high pressure. In other words, an elastic force is generated by the spring member so as to bias the pump body in the axial direction, so that the movement of the pump body in the axial direction is restricted and the damage of the pump casing may be prevented.
According to another prior art, for example, as disclosed in Japanese Patent Publication No. 2002-087236, a high pressure fluid passage communicated to a discharge side of a rotary pump is formed in a housing. And a space is formed between a pump body and a bottom surface of a recessed portion of the housing (into which the pump body is inserted), namely a second back pressure chamber (which has a larger diameter than that of a first back pressure chamber formed at an inlet side, and which surrounds the first back pressure chamber formed at an inlet side) is formed at an axial forward end of the pump body. A high pressure of the working fluid is applied to the space, so that a force for biasing the pump body in a direction opposite to an insertion of the pump body is applied to the pump body. As a result, a movement of the pump body in the direction of insertion is restricted and a casing of the pump body is prevented from being damaged.
According to the above prior art (JP 2007-125929), the force for pushing the pump body is obtained by the spring member. Therefore, since such force is applied to the pump body and the housing irrespective of the internal fluid pressure of the pump body, the pump body and the housing should have rigidity enough to resist the spring force. There are some restrictions for parts and components which constitute the pump body in order to achieve the necessary rigidity. There are other restrictions for processes, according to which the pump body should be assembled while a spring force is adjusted.
The force (pressure) for pushing the pump body in its axial direction is decided based on the spring force and fluid pressure generated in the pump device. In a case that fluid pressure for wheel cylinders of only one hydraulic system (among two hydraulic systems) is increased, while the fluid pressure for wheel cylinders of the other hydraulic system is not increased, the high pressure is generated only in the one hydraulic system. Therefore, the force (pressure) for pushing the pump body may be rather small. On the other hand, in a case that the fluid pressure for the wheel cylinders of both of two hydraulic systems is increased, the force (pressure) for pushing the pump body becomes larger. Therefore, it is necessary for the pump body and the housing to have rigidity enough to resist such high pressure.
According to the above other prior art (JP 2002-087236), in which the high pressure is introduced at the axial forward end surface of the pump body, the high pressure is only introduced into the second back pressure chamber (which surrounds the first back pressure chamber of the inlet side). In other words, a surface area of the axial forward end of the pump body to which the high pressure is applied is rather small, and thereby only insufficient pushing force (pressure) may be applied to the pump body. When the pushing force is smaller, a difference may be generated between the pushing force at the outside of the pump body and an internal fluid pressure of the pump body. Then, a deformation of the casing for the pump body may occur, and gaps between parts for forming the casing may be increased. Therefore, there may be a danger of decreasing pump efficiency.